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Invasive alien species are a growing threat to biodiversity, and identifying the mechanisms that enable these species to establish viable populations in their new environment is paramount for management of the problems they pose. Using an unusually large number of both failed and successful documented introductions of parakeets (Aves: Psittacidae) in Europe, we test two of the major hypotheses on the establishment success of invading species, namely the climate-matching and the human-activity hypothesis. European human population centres where ring-necked parakeet (Psittacula krameri) and/or monk parakeet (Myiopsitta monachus) introductions have occurred. Data on ring-necked and monk parakeet introductions in Europe were gathered from various sources, including published books and articles, but also from unpublished reports and local grey literature. Information was verified with experts from the region under consideration. In order to test the climate-matching hypothesis, we verified whether the climatic factors that determine the parakeets' native ranges also explain establishment success in Europe. Parakeet occurrence data from the native ranges were analysed using the presence-only modelling method M axent, and correlations between parakeet establishment and climatic and anthropogenic variables in Europe were assessed using both stepwise logistic regression and the information-theoretic model selection approach. The establishment success of ring-necked and monk parakeets was found to be positively associated with human population density, and, both in the native and in the introduced regions, parakeet occurrence was negatively correlated with the number of frost days. Thus, parakeets are more likely to establish in warmer and human-dominated areas. The large number of independent parakeet introductions in Europe allows us to test the often-used climate-matching and human-activity hypotheses at the species level. We show that both hypotheses offer insight into the invasion process of monk and ring-necked parakeets. Our results suggest that, in the future, parakeet establishment probability may increase even further because global warming is likely to cause a decrease in the number of frost days and because urbanization and human populations are still increasing.

Aim: Although global trade is implicated in biological invasions, the assumption that trade networks explain the large-scale distributions of non-native species remains largely untested. We addressed this by analysing relationships between global trade networks and plant pest invasion. Location: Forty-eight countries in Europe and the Mediterranean. Time period: Current. Major taxa studied: Four hundred and twenty-two non-native plant pests (173 invertebrates, 166 pathogens, 83 plants). Methods: Ten types of connectivity index were developed, representing potential roles of trade networks, air transport links, geographical proximity, climatic similarity and source country wealth in facilitating invasion. Generalized linear mixed models (GLMMs) identified the connectivity index that best explained both historical and recent invasion. Then, more complex GLMMs were developed including connectivity through trade networks for multiple commodities relevant for pests (live plants, forest products, fruit and vegetables and seeds) and species' transport associations with those commodities. Results: Total import volumes, species' global prevalence and connectivity measures based on air transport, geographical distance or climate did not explain invasion as well as connectivity through global trade networks. Invasion was strongly promoted by agricultural imports from countries in which the focal species was present and that were climatically similar to the importing country. However, live plant imports from nearby countries provided a better explanation of the most recent invasions. Connectivity through multiple trade networks predicted invasion better than total agricultural trade, and there was support for our hypothesis that species known to be transported with a particular network had greater sensitivity to its connectivity. Main conclusions: Our findings show that patterns of invasion are governed to a large extent by global trade networks connecting source areas for non-native species and the dispersal of those species through multiple trade networks. This enhances potential for developing a predictive framework to improve risk assessment, biosecurity and surveillance for invasions.

The literature on biological invasions is biased in favour of invasive species – those that spread and often reach high abundance following introduction by humans. It is, however, also important to understand previous stages in the introduction'naturalization invasion continuum (‘the continuum’), especially the factors that mediate naturalization. The emphasis on invasiveness is partly because most invasions are only recognized once species occupy large adventive ranges or start to spread. Also, many studies lump all alien species, and fail to separate introduced, naturalized and invasive populations and species. These biases impede our ability to elucidate the full suite of drivers of invasion and to predict invasion dynamics, because different factors mediate progression along different sections of the continuum. A better understanding of the determinants of naturalization is important because all naturalized species are potential invaders. Processes leading to naturalization act differently in different regions and global biogeographical patterns of plant invasions result from the interaction of population-biological, macroecological and human-induced factors. We explore what is known about how determinants of naturalization in plants interact at various scales, and how their importance varies along the continuum. Research that is explicitly linked to particular stages of the continuum can generate new information that is appropriate for improving the management of biological invasions if, for example, potentially invasive species are identified before they exert an impact.

Aim We employed a climate‐matching method to evaluate potential source regions of freshwater invasive species to an introduced region and their potential secondary spread under historical and future climates. Location Global source regions, with primary introductions to the Laurentian Great Lakes and secondary introductions throughout North America. Methods We conducted a climate‐match analysis using the CLIMATE algorithm to estimate global source freshwater ecoregions under historical and future climates with an ensemble of global climate models for climate‐change scenario SSP5‐8.5. Given existing research, we use a climate match of ≥71.7% between ecoregions to indicate climatic conditions that will not inhibit the survival of introduced freshwater organisms. Further, we estimate the secondary spread of freshwater invaders to the ecoregions of North America under historical and future climates. Results We identified 54 global freshwater ecoregions with a climate match ≥71.7% to the recipient Laurentian Great Lakes under historical climatic conditions, and 11 additional ecoregions were predicted to exceed the threshold under climate change. Three of the 11 ecoregions were located in South America, a continent where no matches existed under historical climates and eight were located in the southern United States, southern Europe, Japan and New Zealand. Further, we identify 34 North American ecoregions of potential secondary spread of freshwater invasions from the Great Lakes under historical climatic conditions, and five ecoregions were predicted to exceed the threshold under climate change. Main Conclusion We provide a climate‐match method that can be employed to assess the sources and spread of freshwater invasions under historical and future climate scenarios. Our climate‐match method predicted increases in climate match between the recipient region and several potential source regions, and changes in areas of potential spread under climate change. The identified ecoregions are candidates for detailed biosecurity risk assessments and related management actions.

Aim We assess climate similarity among global freshwater and terrestrial ecoregions under historical and future climate scenarios to determine where climate change will impact the climate filter of invasion process. Location Global. Methods We used the Climatch algorithm to conduct a climate‐match analysis to quantify the climate similarity between freshwater and terrestrial ecoregions of the world. Climate match was modelled between all freshwater and terrestrial ecoregions. The analysis was conducted under historical climates and projected climates of 2081–2100 (2090) under three shared socioeconomic pathways SSP2‐4.5, SSP3‐7.0, SSP5‐8.5. Climate matches of each ecoregion were presented as mean climate match to all other ecoregions of the same set. Friedman's non‐parametric rank sum two‐way analysis of variance with repeated measures was used to examine differences in mean climate match between climate scenarios. Results Mean climate match of ecoregions was projected to increase significantly with small effect sizes for freshwater ecoregions (recipients: 0.132; sources: 0.105), and moderate and small effect sizes for terrestrial ecoregions (recipients: 0.330; sources: 0.259). Climate change was predicted to increase mean climate match in North America and Eurasia, particularly in the Arctic by 2090 under each SSP. Ecoregions in central Africa and South America were predicted to have reduced mean climate match. Ecoregions within larger countries (e.g. Australia, Canada, USA) showed variation in mean climate match. Main Conclusion Climate change projections of bioclimatic predictors of species invasions were shown to increase in homogeneity under higher emissions scenarios. Furthermore, we demonstrate how climate change will provide opportunities for invasive species transported among ecoregions to survive under new conditions and identify where the climate filter of the invasion process will be most affected. Findings can be used to inform conservation actions for mitigating the impacts of introduced species by identifying potential risky source regions of future freshwater and terrestrial invasions under climate change.

Plant community response to climate change ranges from synchronous tracking to strong mismatch. Explaining this variation in climate change response is critical for accurate global change modeling. Here we quantify how closely assemblages track changes in climate (match/mismatch) and how broadly climate niches are spread within assemblages (narrow/broad ecological tolerance, or “filtering”) using data for the past 21,000 years for 531 eastern North American fossil pollen assemblages. Although climate matching has been strong over the last 21 millennia, mismatch increased in 30% of assemblages during the rapid climate shifts between 14.5 and 10 ka. Assemblage matching rebounded toward the present day in 10%–20% of assemblages. Climate-assemblage mismatch was greater in tree-dominated and high-latitude assemblages, consistent with persisting populations, slower dispersal rates, and glacial retreat. In contrast, climate matching was greater for assemblages comprising taxa with higher median seed mass. More than half of the assemblages were climatically filtered at any given time, with peak filtering occurring at 8.5 ka for nearly 80% of assemblages. Thus, vegetation assemblages have highly variable rates of climate mismatch and filtering over millennial scales. These climate responses can be partially predicted by species’ traits and life histories. These findings help constrain predictions for plant community response to contemporary climate change.

Aim Thousands of non‐native species have established populations and spread in outdoor environments (i.e., Naturalised), yet some populations or species only occur indoors, potentially due to unsuitable climates. We assessed the hypothesis that non‐native ants are more often restricted to indoor environments when they invade regions with climates dissimilar from their native regions. Furthermore, we forecasted how climate change could influence the naturalisation of indoor‐restricted non‐native ants. Location Global. Methods Using a global database of 323 non‐native ant taxa across 477 regions, we modelled how average climatic conditions in the native and invaded regions of each taxon determined whether they naturalised or were restricted indoors. We then modelled regional climatic suitability for the naturalisation of indoor‐restricted non‐native ants and projected future changes under climate change scenarios. We further assessed if climate change would facilitate the naturalisation of impactful non‐native ants using a global database describing their known impacts. Results Non‐native ants originating from warm regions were more likely restricted indoors when introduced to cold regions. Under 2°C and 4°C of warming, the number of indoor‐restricted non‐native ant species projected to find suitable regional climates for naturalisation increased by an average of 0.08 (maximum = 1.2) and 0.27 (maximum = 3.7) taxa per region, respectively. These anticipated naturalisations include high‐impact non‐native ants, such as the Argentine ant Linepithema humile and are expected to increase socioeconomic and environmental impacts under both warming scenarios, particularly in European regions. Main Conclusions Our findings suggest that indoor environments serve as microclimatic beachheads for biological invasions, especially in cold regions in the Northern Hemisphere. Failure to limit climate warming and inadequate biosecurity management in indoor environments may facilitate the naturalisation of non‐native ants, with costly repercussions on nature and society.

Two Mexican leaf-feeding beetles, Zygogramma piceicollis (Stål) and Zygogramma signatipennis (Stål) (Coleoptera: Chrysomelidae), were released in South Africa for the biological control of the invasive species Tithonia rotundifolia (Mill.) S.E. Blake (Asteraceae: Heliantheae). The aim of this study was to predict the potential of these beetles to establish and spread in South Africa, using MaxEnt climate modelling that incorporated locality data recorded in Mexico between 2008 and 2019 and data from the Global Biodiversity Information Facility. Zygogramma signatipennis displayed a wider distribution than Z. piceicollis in Mexico, with some overlap between the two species. The average receiver operating characteristic curves obtained for Z. piceicollis and Z. signatipennis predicted high mean area under curve values of 0.910 and 0.885, respectively. Jackknife tests revealed that mean annual temperature had the highest gain when used in isolation for Z. piceicollis , compared with minimum precipitation of the driest month for Z. signatipennis . These tests also revealed that the highest and lowest contributing environmental variables for Z. piceicollis and Z. signatipennis were minimum precipitation of the driest month (37.9 and 46.7%) and maximum annual temperature of the warmest month (3.8 and 12.3%), respectively. MaxEnt modelling predicted that at least six of South Africa’s nine provinces provide regions that would support the proliferation of both beetles, with conditions best suited for Z. piceicollis . Despite predictions that both beetles should establish throughout the range of T. rotundifolia in South Africa, their realized establishment has so far been poor. Other factors, besides climate, including release size, site destructions, drought, soil moisture and texture could be constraining establishment.

The damaging effects of invasive organisms have triggered the development of Invasive Species Predictive Schemes (ISPS). These schemes evaluate biological and historical characteristics of species and prioritize those that should be the focus of exclusion, quarantine, and/or control. However, it is not clear how commonly these schemes take microevolutionary considerations into account. We review the recent literature and find that rapid evolutionary changes are common during invasions. These evolutionary changes include rapid adaptation of invaders to new environments, effects of hybridization, and evolution in recipient communities. Strikingly, we document 38 species in which the specific traits commonly associated with invasive potential (e.g. growth rate, dispersal ability, generation time) have themselves undergone evolutionary change following introduction, in some cases over very short (

Species distribution models (SDMs), which statistically relate species occurrence to climatic variables, are widely used to identify areas suitable for species growth under future climates and to plan for assisted migration. When SDMs are projected across times or spaces, it is assumed that species climatic requirements remain constant. However, empirical evidence supporting this assumption is rare, and SDM predictions could be biased. Historical humanaided movements of tree species can shed light on the reliability of SDM predictions in planning for assisted migration. We used Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), a North American conifer introduced into Europe during the mid-19th century, as a case-study to test niche conservatism. We combined transcontinental data sets of Douglas-fir occurrence and climatic predictors to compare the realized niches between native and introduced ranges. We calibrated a SDM in the native range and compared areas predicted to be climatically suitable with observed presences. The realized niches in the native and introduced ranges showed very limited overlap. The SDM calibrated in North America had very high predictive power in the native range, but failed to predict climatic suitability in Europe where Douglas-fir grows in climates that have no analogue in the native range. We review the ecological mechanisms and silvicultural practices that can trigger such shifts in realized niches. Retrospective analysis of tree species introduction revealed that the assumption of niche conservatism is erroneous. As a result, distributions predicted by SDM are importantly biased. There is a high risk that assisted migration programs may be misdirected and target inadequate species or introduction zones.